Backup safety flow control system for concentric drill string

Abstract

A technique is presented for providing a double-barrier to formation fluids during drilling operations with a concentric drill string having an inner bore and an annulus. A primary flow control system is used to provide a first barrier to formation fluids in the inner bore and annulus of the drill string. A backup flow control system is used to provide a second barrier to formation fluids. The backup flow control system comprises a backup inner bore shutoff valve and a backup annulus shutoff valve. The backup inner bore shutoff valve is dropped from the surface through the inner bore of the drill string. The backup inner bore shutoff valve has spring-biased tabs that are configured to extend outward to contact an inner surface profile of the inner bore of the drill string. The backup annulus shutoff valve may be provided with the profile to receive the spring-biased tabs from the backup inner bore shutoff valve. When the tabs of the backup inner bore shutoff valve are disposed opposite the profile, the tabs of the backup inner bore shutoff valve are extended outward into the profile by a spring assembly, securing the backup inner bore shutoff valve within the drill string.

Description

BACKGROUND[0001]The invention relates generally to shutoff valves for wells. In particular, the invention relates to a backup shutoff valve system for a concentric drill string and a method for installing and using the backup shutoff valves in a concentric drill string.[0002]Most oil and gas wells are drilled with a rotary drilling rig. Typically, the drilling rig uses a string of drill pipe with a drill bit on the end. The drill string is rotated by the rotary drilling rig to rotate the drill bit into the ground. A drilling fluid is used to maintain control of the wellbore fluids in the well, as well as to remove the cutting from the wellbore. The drilling fluid may be pumped down the interior passage of the drill pipe, so that it may exit the drill bit through nozzles in the drill bit. The drilling fluid and cuttings are returned to the surface in the annulus space surrounding the drill pipe in the wellbore.[0003]In many cases, the drilling fluid is a liquid known as drilling mud....

AI Technical Summary

Benefits of technology

[0007]A technique is presented for providing a double-barrier to formation fluids in a concentric drill string having an inner bore and an annulus. The technique prevents formation fluids from flowing uncontrollably upward through the concentric drill string to the surface. The first barrier to formation fluids is a primary flow control system that is provided to prevent formation fluids from flowing to the surface during a well excursion. The primary flow control system comprises a primary inner bore shutoff valve and a primary annulus shutoff valve. The primary inner bore shutoff valve may be used to block fluid flow through the inner bore of the concentric drill string. The primary annulus shutoff valve may be used to block fluid flow through the annulus of the concentric drill string.

Problems solved by technology

However, drilling mud can damage the formation around the wellbore, thereby reducing the ability to retrieve fluids later when the well is put into production.

If liquid drilling mud is used, the coal beds may be damaged by the encroaching drilling mud from the wellbore.

Because a column of air does not have the hydrostatic pressure of heavy drilling mud, valve assemblies have been developed to control the flow of fluid within the inner drill string and in the annulus between the inner and outer drill strings in the event that formation fluid begins to flow into the drill string, such as during a blowout or “kick.” However, problems have been experienced with these valve assemblies.

For example, these drill string valve assemblies have been known to leak.

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